42 PROCEEDINGS OF THE ACADEMY OF [1890. 



very minute, slender teeth, almost obsolete. A complete half row of 

 teeth is figured on the plate. 



The characters of the radula prove, as I had anticipated, that this 

 species and A. knys7iaensis are congeneric, forming a group exhib- 

 iting characters distinct from all other agnathous genera. Com- 

 jjared with knysnaensis, the A. caffra differs in the greater speciali- 

 zation of the radula, seen in the reduction of the lateral teeth to five 

 on each side, instead of twelve ; and in the smaller outer laterals. I 

 do not regard the minute teeth lying outside of the fifth lateral as 

 " marginals" or uncini, but as degenerate lateral teeth ; true uncini 

 being absent in the Agnatha, which in this respect hold somewhat 

 the same relation to the Gnathojyhora that Rhachiglossa or Toxo- 

 glossa bear toward Tcenioglossa. In the characters of radula, Aerope 

 caffra represents the highest specialization of agnathous snail yet 

 made known. The characteristics of the Agnatha, — oblique rows of 

 thorn-shaped teeth, becoming smaller toward the center and the outer 

 edges of the radula — are here exaggerated. In no hitherto known 

 genus are the functional lateral teeth so few, or the outer ones so 

 nearly lost.^ In no other genus is there so abrupt a break in the 

 size of the lateral teeth. The tendency in Agnatha seems to be to- 

 ward a type of radula analogous to that represented in Pectini- 

 branchs by the Toxoglossa. 



The genitalia have considerable resemblance to those of A. knys- 

 ■na'ensis. The vas deferens is curiously convoluted just below the 

 twisted portion of the oviduct (see fig. f). The albumen gland (a. 

 £/.) is very large, but perhaps more swollen in my figures than in a 

 freshly killed animal. I did not find any spermatheca, but think 

 that this was owing to the soft, partly decayed condition of the vis- 

 cera. I did not dissect out the ovo-testis. The orifice of the gene- 

 talia is very near the right tentacle. 



The blind sac opening below the mouth, supposed by Dr. Leidy 

 to be the seat of the olfactory sense, is very long, folding upon it- 

 self, terminating in the muscular tissues of the foot about one-third 

 the length of the latter from the posterior extremity. When ex- 

 tended the length of the sac is about 100 mm. 



1 Rhytida may be considered more specialized in one respect: — the absence of 

 a rhaciiidian tooth. 



